Both during and following fabrication, integrated circuit manufacturers test the integrated circuits to determine that they satisfy design specifications. These tests typically involve the use of test probe cards that use test heads comprising a plurality of pins. The test pins are usually needles or metal blades that make electrical contact with test pads on the integrated circuits.
Conventional test heads that use needles or metal blades suffer from several limitations. As integrated circuits increase in both size and complexity, both the number of test pads on the circuit and the number of pins on the test head for testing the circuits must increase. Also, the input and output speed of test signals must increase with increasing the speed of devices. With these requirements, conventional integrated circuit testing devices have input/output limitations that are incompatible or insufficient to meet the testing needs of new and more complex integrated circuits. Moreover, as the number of pins increases their likelihood of being misaligned, bent, or shorted together increases.
Consequently, convention test probes that manufacturers use to test complex integrated circuits have short functional lives. Yet another limitation of conventional test heads is that the pins they use are metallic and have significant length relative to their signal wavelengths. As a result, they suffer from capacitance and inductance limitations that reduce the speed of input/output between integrated circuit and the testing circuitry. There are no known ways to reduce this type of parasitic impedance mismatch to thereby increase test signal input/output rates between the integrated circuit and the test circuitry.
Testing systems are also becoming increasingly automated and complex. Automated prober systems for integrated circuits help to reduce operator intervention during the test process. New prober systems offer greater accuracy and longer life, and improve productivity through features such as automatic wafer alignment and profiling. Some of the latest probers incorporate on-line systems which automatically evaluate and correct, if necessary, testing circuitry features such as contact impedance. These systems can accommodate even more complex test probe cards than are presently available.
In an attempt to solve the limitations inherent in conventional integrated circuit test heads, a thin film test probe is described in C. Barsotti et al., "New Probe Cards Replace Needle Types," Semiconductor International, p. 98 (Aug. 1, 1988). That device (the "Barsotti device") produces a high density and high performance and uses a metallic contact pad configuration to provide a more reliable test signal communication path and decrease parasitic capacitance and inductance in test signal transmission. The Barsotti device includes a test probe that comprises an elastomer base with a ground plane and a thin polyimide layer covering the ground plane for insulating the ground plane from the elastomer base. Micro-strip lines cover the polyimide layer and connect to the metallic contact pads. The metallic contact pads engage test pads on the integrated circuit to be tested.
Though the Barsotti device represents and improvement in integrated circuit testing technology, it still suffers from severe limitations. The Barsotti device increases the performance of integrated circuit testing, but at a significantly increased cost to the tester. Other limitations associated with that test include, first of all, that the elastomer based test probe requires the use of nonconventional fabrication techniques. Additionally, the polyimide and ground plane layers of the Barsotti device are bent to provide a protruded surface from which the metallic contact pads can extend.
Consequently, there is the need for an integrated circuit test head that provides high density and high performance integrated circuit testing at a substantially lower cost than known test heads.
There is also a need for an integrated circuit test head that uses known semiconductor device techniques to reliably produce high density and high performance integrated circuit testing.